Bead-stiffened composite parts

ABSTRACT

A beaded composite panel is fabricated using composite plies. An opening is formed in each of plies, and each ply is laid up on a bead feature and drawn down over the bead feature in the area of the opening so as to widen the opening into a gap allowing the ply to conform to the contour of the bead feature. Patches are fabricated and placed on the plies overlying over the openings. The laid-up plies are compacted and cured.

This application is a divisional of application Ser. No. 12/409,742,filed Mar. 24, 2009.

BACKGROUND INFORMATION

1. Field

The disclosed embodiments generally relate to stiffened composite parts,and deal more particularly with a method of fabricating beaded compositepanels.

2. Background

Composite parts such as panels may be stiffened to resist bendingmoments using a variety of techniques. One such technique involvesforming integral structural features, referred to as “beads”, into thepanel during layup. Bead-stiffened panels may be fabricated by laying upprepreg plies on a tool that includes raised bead features on a toolsurface that determines the shape into which the panel is formed. Thetool may also be used to compact and cure the layup.

Beads of sufficiently effective height may be difficult to form becauseof the difference in effective length that the fibers in the ply mustcover; some fibers extend over the flat areas of the tool while otherfibers must extend up and over the bead features. Also ply wrinkling mayresult in the transition areas between different developed fiberlengths.

One solution to the problem mentioned above involves using larger piecesof prepreg than would otherwise be necessary, which are hand-worked downover the bead features while attempting to smooth out wrinkles and avoidexcessive applied tension. Another solution involves sandwichingcomposite plies between sheets of a carrier material such as aluminumsheet metal which are used to mechanically force the plies down over thebeads features while maintaining tension in the sandwich. Thistechnique, however, requires the use of specialized equipment and limitsthe size of the panel to that of the equipment while requiring moreconsumable materials that are single use. Moreover, because the formingprocess is hidden from view until it is completed, problems such as plywrinkling, deformation or breakage may not be detected until the ply hasbeen formed. Still another method involves using specialized“extra-formable” material forms, however these forms are more costlythan standard materials and may not be approved or qualified for use informing certain types of parts.

Accordingly, there is a need for a method of making bead-stiffenedcomposite parts using standard materials and relatively simple toolswhich may reduce or substantially eliminate wrinkling and/orunacceptable distortion of ply materials during the bead formingprocess.

SUMMARY

The disclosed embodiments provide a method of fabricating a beadedcomposite part, such as a beaded panel, using conventional materials andsimplified layup tooling. Wrinkling and/or undesirable distortion of plymaterials is reduced or eliminated by cutting slits in the plies whichallow the ply material to more readily conform to bead features formingpart of the tool. Although the slits widen into gaps in the ply as theply material is being formed over bead features in the tool, sufficientstructural strength and stiffness of the resulting beaded panel ismaintained by filling and covering the gaps with composite patchesduring the layup process.

According to one disclosed embodiment, a method is provided of laying upa beaded composite part. The method includes forming an opening in atleast one ply and placing the ply on a tool having a raised beadfeature, including aligning the opening over the bead feature. A patchis fabricated and placed over the opening in the ply. The opening may beformed by cutting a slit in the ply and cutting darts in the ply at theends of the slit. The patch may be fabricated by cutting a piece ofprepreg cloth into a shape that covers both the slit and the darts.

According to another embodiment, a method is provided of fabricating abeaded composite panel. The method includes cutting a slit in each of aplurality of plies, and laying up the plies on a bead tool, includingplacing the slit in each ply over a bead feature on the tool. Each ofthe plies is drawn down over the bead feature in the area of the slit soas to widen the slit into a gap, allowing the ply to conform to thecontours of the bead feature. The method also includes at leastpartially filling the gap with a filler and fabricating patches that areplaced on the plies, overlying the filler. Following layup, the pliesare cured.

A further embodiment provides a method of fabricating a beaded compositepanel. The method includes providing a plurality of unidirectional fiberreinforced prepreg plies and cutting at least one slit in each of theplies in an area where a bead is to be formed. The plies are laid up ona tool having at least one raised bead feature and the slits in each ofthe plies are forced down over the bead feature. The slits in each ofthe plies are covered with a prepreg cloth, following which the pliesare compacted and cured.

The disclosed embodiments satisfy the need for an improved method ofmaking a beaded composite part, especially composite panels whichreduces or eliminates wrinkling and/or undesirable stretching ofmaterial during the layup process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a perspective view of a typical compositebeaded panel.

FIG. 2 is an illustration of an exploded view of a bead tool, a slit plyand patches.

FIG. 3 is an illustration of a sectional view taken along the line 3-3in FIG. 2.

FIG. 4 is an illustration of a flow diagram of a method of fabricating abeaded panel.

FIG. 5 is an illustration of a perspective view of a portion of a slitply being placed onto a bead tool feature.

FIG. 6 is an illustration of a perspective view similar to FIG. 5, butshowing the ply having been drawn down over the bead feature.

FIG. 7 is an illustration of a perspective view similar to FIG. 6 butshowing an optional filler having been placed in a gap formed bywidening of the slit.

FIG. 8 is an illustration of a perspective view similar to FIG. 7 butshowing a patch being readied for placement over the slit.

FIG. 9 is an illustration of a perspective view similar to FIG. 8, butshowing the patch having been placed on the ply and covering the slit.

FIG. 10 is an illustration of a plan view of several overlying patcheshaving edges staggered relative to each other.

FIG. 11 is an illustration of a flow diagram of aircraft production andservice methodology.

FIG. 12 is an illustration of a block diagram of an aircraft.

DETAILED DESCRIPTION

Referring first to FIG. 1, the disclosed embodiments provide a method offabricating a part such as a beaded panel 20 formed of laminated pliesof fiber reinforced polymer resin such as, without limitation, carbonfiber epoxy. The plies may be unidirectional fiber reinforced prepreg,or a dry, tackified cloth reinforcement that is laid up and subsequentlyinfused with a polymer resin. The fiber reinforcement and the polymerresin comprising the plies may be any of a wide range of knownmaterials. In the illustrated embodiment, the body 22 of the panel 20 isessentially flat, however the body 22 may have one or more curves orcontours (not shown), depending upon the application. The panel 20 maybe stiffened against bending moments about an axis substantiallyparallel to axis 23 by means of a plurality of beads 24 which areintegrally formed into the body 22 of the panel 20 by a method describedbelow. In this example, the beads 24 are elongate, and have theirlongitudinal axes 25 substantially aligned substantially perpendicularto the axis 23 of the panel 20. The number, size, pattern, alignment andlocation of the beads 24 may vary, depending on the application. Forexample, the beads 24 may be aligned in any direction relative to theaxis 23. Groups of the beads may be staggered relative to each other,and may be arranged in patterns that are regular or irregular, or acombination of both. For example, the beads 24 could be staggeredrelative to each other, rather than being aligned as shown in FIG. 1, soas to increase the bending stiffness of the panel 20 about axis 23.

Referring now to FIG. 2, the beaded panel 20 shown in FIG. 1 may befabricated by laying up a plurality of plies 42 on a tool 56. Each ofthe plies 42 may be a unidirectional or bidirectional fiber reinforcedprepreg, or a dry cloth (not shown) which is later infused with resin.In the example illustrated in FIG. 2, the ply 42 is a 0 degreeunidirectional prepreg. The plies 42 may be laid up on the tool 56according to a predefined ply schedule (not shown) which may define thenumber and layup orientation sequence of the plies 42, as well as theparticular type of material used in each ply 42.

The tool 56 may include a plurality of raised bead features 58 which aregenerally similar in shape to the beads 24 formed in the panel 20 shownin FIG. 1. As seen in FIG. 3, each of the bead features 58 is raisedabove a tool surface 57 by a height “h” and may include contoured sides60 extending around the entire perimeter of the bead feature 58. In theexample shown in FIG. 3, each of the bead features 58 has a crosssection that is generally bell-shaped, however the cross sectional shapeas well as the contours 60 of the bead features 58 may vary, dependingupon the application, and the particular type of bead 24 that is to beformed in the panel 20.

Each of the plies 42 has an opening 44 formed therein at locations whichoverlie the bead features 58 when the ply 42 has been laid up on thetool 56. As will be discussed below in more detail, each of the openings44 may include an elongate slit 46 and a pair of darts 48 on each end ofthe slit 46. The slits 46 and the darts 48 are strategically locatedsuch that forming of the plies 42 is confined mostly to single curvatureforming, which may reduce wrinkles. Wrinkling may also be reduced as aresult of the fact that the reinforcing fibers in the ply 42 do not haveto traverse the entire additional length up and over the bead feature58.

After the ply or plies 42 has been drawn down onto the tool 56, dry orprepreg cloth patches 50 are placed on the ply 42 covering the openings44. In the illustrated example, the patches 50 are generally “dog-bone”shaped, comprising an elongate medial portion 54 which is intended tocover the slit 46, and enlarged, generally semi-circular end portions 52which are respectively intended to cover the darts 48. Because thepatches 50 are formed of cloth material, they may more easily conform tothe compound curvature 60 a at the ends of the bead features 58. Thepatches 50 function to splice together the open darts 48 in theunderlying plies 42.

Referring now to FIGS. 4 and 5, a method of fabricating the beaded panel20 (FIG. 1) begins at step 26 in which the openings 44 are formed in theply 42. The openings 44 have a predetermined pattern, which in theillustrated example, as previously mentioned, comprise a slit 46 anddarts 48 at the end of each slit 46. The slits 46 are substantiallyaligned with the central axis 65 of each bead feature 58. In someapplications, it may be desirable to slightly stagger the openings 44 inthe plies 42 so that the openings 44 are not vertically aligned insubsequently laid up plies 42. The slits 46 and darts 48 may be formedusing any of various equipment, such as without limitation, lasercutters, die cutters, or other automated ply cutting equipment andtechniques (all not shown) which may reduce processing times and improvepart consistency.

Next, at 28, the ply 42 is placed on the bead containing tool 56 asshown in FIG. 6 and the slit 46 and darts 48 are drawn down over thebead feature 58 at step 30. As the ply 42 is drawn down over the beadfeature 58, the slit 46 and darts 48 allow the ply 42 to spread in thearea surrounding the opening 44 so as to better conform to the contours60 of the tool feature 58 and release tension in those fibers that wouldotherwise be required to travel up and over the bead feature 58. The ply42 may be swept by hand or equipment so as to smooth any wrinkles (notshown) that might be present in the ply 42. As the ply 42 is drawn downonto the bead feature 58, the slit 46 may widen to form a gap “G”.

Referring now to FIGS. 4 and 7, in some applications it may be desirableto at least partially fill the gap G. In order to fill or partially fillthe gap G, an optional filler strip 62 of dry cloth or unidirectionalprepreg, may be cut as shown at step 32 in FIG. 4, and placed in the gapG as shown in FIG. 7, thereby filling or partially filling the gap Gformed by the widened slit 46. In some applications, the filler strip 62may not be necessary.

Referring now to FIGS. 4 and 8, at step 34, the patch 50 may be cut froma sheet (not shown) of dry or prepreg cloth such that the dimensions ofthe medial portion 52 and end portions 54 are sufficient to cover thefiller strip 62 and the darts 48.

Next, as shown in FIGS. 4 and 9, the patch 50 is placed over the fillerstrip 62 and darts 48, as shown at step 36. The patch 50 may be smootheddown over the contours 60 of the bead feature 58 so as to conformallycover the entire opening 44. As shown in FIG. 10, the end portions 54 ofthe patches 52 may be sized and cut so that the shape of their outeredges 64 are slightly different from each other. As a result, when theplies 42 are stacked, the outer edges 64 of the patches 52 are slightlystaggered so as to minimize the local build-up of material within thelayup, and improve the structural integrity of the stack.

Additional plies 42 are laid up, as shown at 38 in FIG. 4, by repeatingsteps 26-36 until all of the plies 42 have been laid up according to theapplicable ply schedule. The completed layup may be compacted and curedat step 40.

Embodiments of the disclosure may find use in a variety of potentialapplications, particularly in the transportation industry, including forexample, aerospace, marine and automotive applications. Thus, referringnow to FIGS. 11 and 12, embodiments of the disclosure may be used in thecontext of an aircraft manufacturing and service method 70 as shown inFIG. 11 and an aircraft 72 as shown in FIG. 12. During pre-production,exemplary method 70 may include specification and design 74 of theaircraft 72 and material procurement 76 in which the disclosed methodmay be specified for use in fabricating beaded parts. During production,component and subassembly manufacturing 78 and system integration 80 ofthe aircraft 72 takes place. The disclosed method and apparatus may beused to fabricate beaded parts or components that are then assembled andintegrated with other subassemblies. Thereafter, the aircraft 72 may gothrough certification and delivery 82 in order to be placed in service84. While in service by a customer, the aircraft 72 is scheduled forroutine maintenance and service 86 (which may also include modification,reconfiguration, refurbishment, and so on). Beaded components fabricatedby the disclosed method may be used to replace components on theaircraft 72 during the maintenance and service 86.

Each of the processes of method 70 may be performed or carried out by asystem integrator, a third party, and/or an operator (e.g., a customer).For the purposes of this description, a system integrator may includewithout limitation any number of aircraft manufacturers and major-systemsubcontractors; a third party may include without limitation any numberof vendors, subcontractors, and suppliers; and an operator may be anairline, leasing company, military entity, service organization, and soon.

As shown in FIG. 12, the aircraft 72 produced by exemplary method 70 mayinclude an airframe 88 with a plurality of systems 90 and an interior92. Examples of high-level systems 90 include one or more of apropulsion system 94, an electrical system 96, a hydraulic system 98,and an environmental system 100. Any number of other systems may beincluded. Although an aerospace example is shown, the principles of thedisclosure may be applied to other industries, such as the marine andautomotive industries.

Systems and methods embodied herein may be employed during any one ormore of the stages of the production and service method 70. For example,beaded components or subassemblies corresponding to production process78 may be fabricated or manufactured in a manner similar to componentsor subassemblies produced while the aircraft 72 is in service. Also, oneor more method embodiments, or a combination thereof may be utilizedduring the production stages 78 and 80, for example, by substantiallyexpediting assembly of or reducing the cost of an aircraft 72.Similarly, one or more method embodiments, or a combination thereof maybe utilized while the aircraft 72 is in service, for example and withoutlimitation, to maintenance and service 86.

Although the embodiments of this disclosure have been described withrespect to certain exemplary embodiments, it is to be understood thatthe specific embodiments are for purposes of illustration and notlimitation, as other variations will occur to those of skill in the art.

What is claimed:
 1. A beaded composite part fabricated by the method of:forming at least one opening in a ply of a prepreg material or acomposite dry fiber cloth; placing the ply on a tool having a raisedbead feature including forcing the opening down over the bead feature soas to substantially conform the ply to the contour of the bead feature;aligning the opening over the bead feature; fabricating a compositepatch; and placing the composite patch over the opening in the ply whileon the raised bead feature.
 2. The beaded composite part of claim 1,wherein forming the opening includes: cutting a slit in the ply, andcutting darts in the ply at the ends of the slit.
 3. The beadedcomposite part of claim 2, wherein fabricating a composite patchincludes: cutting a piece of cloth into a shape having a first portioncovering the slit and second portions covering the darts.
 4. The beadedcomposite part of claim 1, wherein fabricating the patch includes:cutting a piece of prepreg cloth into a shape that substantially coversthe opening.
 5. A beaded composite panel fabricated by: providing pliescomprising a plurality of unidirectional fiber reinforced prepreg plies;cutting a slit in each of the plies in an area where a bead is to beformed; laying up each of the plies on a tool having at least one raisedbead feature; forcing the slit in each of the plies down over the beadfeature; covering the slit with a prepreg cloth patch; compacting theplies; and curing the plies.
 6. The beaded composite panel of claim 5,wherein forcing each of the plies down over the bead feature spreads theslit into a gap, and the beaded composite panel is further fabricatedby: filling the gap by placing a piece of unidirectional fiberreinforced prepreg in the gap, including aligning the fiber orientationof the piece of unidirectional fiber reinforced prepreg with the fiberorientation of the ply.
 7. The beaded composite panel of claim 6,wherein covering the slit includes placing the patch over the piece ofunidirectional fiber reinforced prepreg placed in the gap.
 8. The beadedcomposite panel of claim 5, wherein: the bead feature is elongate, andcutting the slit includes making an essentially straight cut in the plyalong substantially aligned with the longitudinal axis of the beadfeature.
 9. The beaded composite panel of claim 5, wherein the beadedcomposite panel is further fabricated by: cutting darts in the ply ateach end of the slit.
 10. The beaded composite panel of claim 5, whereinforcing the slit down over the bead feature includes smoothing the plyaround the slit to conform to the contour of the bead feature.
 11. Thebeaded composite panel of claim 5, wherein laying up the plies includesstacking the plies respectively in differing layup orientationsaccording to a predefined ply schedule.